1. Field of the Invention
The present invention relates to a hot-air heater which incorporates an air-blowing fan on an upstream side and an electric heater on a downstream side of an air-blowing passage.
2. Description of the Related Art
A conventional hot-air heater has, as described in Jpn. Pat. Appln. KOKAI Publication No. 1998-132385, comprises a frame having an outlet and an inlet formed therein, in which frame an air-blowing passage is formed which leads from the inlet to the outlet. Along this air-blowing passage, there are provided an air-blowing fan on an upstream side and an electric heater constituted of an elongated sheathed heater etc. on an downstream side. In this case, the electric heater is disposed in such a manner as to intersect with air flowing along the air-blowing passage. In this configuration, if the air-blowing fan is operated, air is sucked in the air-blowing passage through the inlet and heated by the electric heater to provide hot air having a predetermined temperature, which is blasted out of the outlet to a room.
In this hot-air heater, an air trunk area of the air-blowing passage is kept constant all along this passage leading from the downstream side of the air-blowing fan to the outlet and the electric heater is provided somewhere along this passage, so that air trunk resistance in this air-blowing passage (i.e., resistance against air flow in the air-blowing passage) is increased by this electric heater, which is a problem. Therefore, it has been proposed to form an expansion on the air-blowing passage so that the expansion may be a storage portion to contain the electric heater. In this case, the electric heater evenly heats air passing through this expansion, so that it may be considered to arrange the electric heaters in a plurality of stages in such a manner that the heater may face an entrance opening in the expansion.
If, as in the case of this hot-air heater, a bent portion is formed along the air-blowing passage and provided with the air-blowing fan, a wind speed of air flowing on an outer side of the bent portion is higher than that of air flowing on an inner side of this bent portion, so that a wind speed distribution in the air-blowing passage between the bent portion and the electric heater does not become constant. Therefore, if the electric heaters are arranged in a plurality of stages along the entrance opening in the expansion, a large quantity of air locally collides with the electric heater positioned on the outer side of the bent portion where the wind speed is high, thus increasing air trunk resistance of the air-blowing passage. In this case, to obtain a sufficient airflow of hot air blasted out of the outlet, it is necessary to increase a rotation speed of a moving vane, thus increasing an operating sound, which is a problem.
In view of the above, it is an object of the present invention to provide a hot-air heater in which an expansion is provided along an air-blowing passage in such a manner that even if electric heaters are arranged on this expansion in a plurality of stages, air trunk resistance may be suppressed from increasing to prevent a rotation speed of an air-blowing fan from increasing for a purpose of obtaining a target airflow, thereby preventing operating sound from increasing.